The present invention relates in general to printing stereoscopic images, multiple images, or motion images; and in particular to a method for printing interdigitated images or a lenticular medium.
Lenticular overlays are a means of giving images the appearance of depth. A lenticular image is created using a transparent upper layer having narrow, parallel lenticules (semi-cylindrical lenses) on an outer surface, and an image-containing media. The two layers form a lenticular system wherein different portions of an image are selectively visible as a function of the angle from which the system is viewed.
If the image is a composite picture made by bringing together into a single composition a number of different parts of a scene photographed from different angles and the lenticules are oriented vertically, each eye of a viewer will see different elements and the viewer will interpret the net result as depth of field. The viewer may also move his head with respect to the image thereby observing other views with each eye and enhancing the sense of depth. When the lenticules are oriented horizontally, each eye receives the same image. In this case, the multiple images give illusion of motion when the composite image is rotated about a line parallel to a line formed by the viewers eyes.
Whether the lenticules are oriented vertically or parallel, each of the viewed images are generated by lines of images which have been interlaced at the frequency of the lenticular screen. Interlacing lines of each image is referred to as interdigitation. Interdigitation can be better understood by using as an example four images used to form a composite with a material having three lenticules. In this example, line 1 from each of the four images is in registration with the first lenticule; line 2 from each of the four images is in registration with the second lenticule; etc. Each lenticule is associated with a plurality of image lines or an image line set, and the viewer sees only one image line of each set with each eye for each lenticule. It is imperative that the image line sets be registered accurately with respect to the lenticules, so that the proper picture is formed when the assembly is viewed.
Conventional recording of linear images on a lenticular recording material has been accomplished with a stereoscopic image recording apparatus that uses optical exposure. A light source, such as a halogen lamp, is projected through an original image, through a projection lens, and focused on lenticular material. The images are exposed on a receiver attached to the lenticular material as linear images. Japanese (Kokoku) Patent Application Nos. 5473/1967, 6488/1973, 607/1974, and 33847/1978 disclose recording apparatus in which two original images are projected for printing on a lenticular recording material. Recording composite images in this fashion requires complex lens structures, which are expensive.
In contrast, image recording by scanning exposure requires comparatively simple optics, has great flexibility in adapting to various image processing operations, and to alterations in the dimension of the lenticules. To take advantage of these features, various apparatus and methods have been proposed for recording image by scanning exposure. For example, Japanese (Kokoku) Patent Application No. 3781/1984 teaches a stereoscopic image recording system in which a plurality of original images is taken with a TV camera, processed and stored in frame memories from which the stored image signals are retrieved sequentially as linear images in accordance with the pitch of lenticular lenses used. After the linear images are recorded on a recording material by scanning exposure, the lenticular sheet is bonded to the recording material. Another scanning method uses polygon scanners, described in U.S. Pat. No. 5,349,419, for exposure of photosensitive stereoscopic images directly on lenticular materials.
In order to manufacture lenticular images, a small spot size and long straight uniform scan lines are needed. U.S. Pat. No. 3,485,945 describes a system for producing high quality lenticular images writing images directly onto the back of lenticular material.
One inherent limitation of direct writing techniques is that in order to achieve large high resolution images the scan lines must be written with a small spot size and must be written as long straight lines. This results in a scan line length to spot size ration, which is so large as to be impractical. As a result, the optical design of the device for scanning the lines which form the image, and which must provide a uniform scan which maintains linearity alignment and spot size specifications throughout its scan length, becomes impractical. Whether the scanning device is a cathode ray tube, a scanned light beam, a scanned beam of electrons, a thermal resistive head, or other image-scanning device, the requirement of small spot size and long, straight, uniform scan lines may not be achievable at a reasonable cost. This problem is aggravated because the scan lines must be parallel to the lenticules or across the lenticules, throughout the entire length of the scan.
To make large, high quality lenticular images requires writing scan lines which are accurately aligned to the lenticular material over the entire of the image. Because the precision required is proportional to the number of views and the size of the lenticules, increasing the size of the lenticules and reducing the number of views has solved the problem in the past. The disadvantage of decreasing the number of lenticules is that the image has lower apparent resolution and the lenticular material must be thicker making the image heavier and more expensive because of the additional material required. Another disadvantage of decreasing the number of views is that all the overall image quality is reduced.
In prior art applications, lenticular views have been digitally written in a single scan thereby limiting the dimensions of the image produced to the size of the printer scan, or necessitating the use of an enlarger which decreases image quality and increases the cost of manufacturing. See Method for Enlarging Images for Lenticular Prints by R. R. A. Morton, U.S. Pat. No. 5,673,100.
It is an object of the present invention to provide a method and apparatus for printing large format lenticular images.
According to one aspect of the present invention, an apparatus for printing large format lenticular images on a lenticular sheet having a plurality a generally parallel lenticules on a front side of the lenticular sheet, comprises a sensor which senses a beginning of each lenticule. A printhead prints interleaved image information on the lenticular sheet in a series of swaths wherein a width of each of the swaths is less than a width of the lenticular sheet. In one embodiment, each of the swaths is printed in a direction parallel to said lenticules. In another embodiment, each of the swaths is printed in a direction perpendicular to said lenticules.
In the preferred embodiment, a narrow scanning spot prints on a silver halide emulsion on a backside of the lenticular sheet. According to another aspect of the invention, the spot is elongated.
An advantage of the present invention is that when printing in swaths perpendicular to the direction of the lenticules, lenticular rows, which are not straight, do not degradate the quality of the image.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.